Patent GB-1150931-A (GB)
Title: Improvements relating to The Arresting Of Electrically Driven Arrangements
IPC: D05B69/22
Filed: 1966-05-27
Abstract: 1,150,931. Controlling clutches; electromagnetic brakes. FRANKL & KIRCHNER FABRIK FUR ELEKTROMOTOREN UND ELEKTRISCHE APPARATE. 27 May, 1966 [28 May, 1965; 16 March, 1966], No. 23789/66. Headings F2E and F2L. [Also in Division H3] A machine is stopped in a predetermined position, for example a sewing machine is stopped in its needle-up or needle-down position, by means of transistorized control circuits for an electromagnetic clutch and an electromagnetic brake through which the machine is driven and which circuits, on the initiation of the stopping process, control the clutch and brake energization to reduce the output speed to a predetermined value and maintain it at this value until the predetermined position is reached whereupon a control signal produces full brake application and complete clutch disengagement. As shown in Fig. 1 a clutch winding MK is in the collector circuit of a transistor T101 and a brake winding MB is in the collector circuit of a transistor T102. During normal running the output speed is controlled by controlling the energization of the clutch winding MK by adjustment of the base current of the transistor T101 by pedal operated switches S30 which determine the resistance in the base circuit. To stop the machine the pedal is released, opening switches S30 and closing switches S20, S10. The base of transistor T101 is now connected via a Zener diode Z to the collector of transistor T102. A control potential is fed to the base of transistor T102 through switch S10 which is composed of a voltage supply by an output driven generator G and an impulse supplied, in the appropriate position of the machine, by a control head S and amplified in a transistor amplifier V. At the initiation of the stopping process the machine is running at high speed and hence the generator provides a relatively high control potential on transistor T102 to give a high braking moment and low clutch energization. When the output speed reaches a predetermined value such as 200 r.p.m. the speed is maintained at this value, any tendency of the speed to fall further reducing the brake application and increasing that of the clutch, and any tendency of speed to increase increasing the braking and reducing the clutching. When the predetermined output position is reached, the signal from the control head S makes transistor T102 fully conducting and transistor T101 fully blocked so that the brake is fully applied and the clutch fully disengaged. In the embodiment shown in Fig. 2 the outputdriven governor G is connected by way of a rectifier to the bases of transistors T3, T4, resistors R7, R8 being switchable into the circuit to adjust the output speed which is maintained during stopping. Control heads O, U can be selectively switched into the circuit to give impulses in the needle-up and needle-down positions of the sewing machine. The emitter of the transistor T3 is connected to the base of a transistor T6 controlling a brake winding MB, and the collector of transistor T4 is connected to the base of a transistor T9 controlling a clutch winding MK. During the stopping operation the potential supplied to the bases of the transistors T3, T4 by the generator G increases the current through transistor T4 thereby reducing the flow through transistor T9 and thus reduces the clutch energization, and the potential, if sufficiently great, makes transistor T3 conducting which in turn makes transistor T6 conducting to apply the brake and reduce the output speed to a predetermined value at which it remains until the signal from the head O or U completely releases the clutch and fully applies the brake. A time delay circuit R1, C1 in the collector circuit of transistor T3 softens the initial brake application. A relay RS3 actuates a magnetic thread cutter F, the operation being initiated only when the machine is stationary in the desired position. In a modification a thread cutter control circuit is provided for thread cutters which are actuated by curved bars in which the machine needs to make one revolution from its stopping position, during which time the thread cutter is operated mechanically.